This is one of the tools used by the medical-nin of Konohagakure. It resembles a rudimentary sniper rifle, which is used to shoot projectiles such as injection shots to put the target to sleep. It consists of a metal tube roughly the size of a ruler with an opening at either end like a blow pipe and is equipped with a scope on top and a laser-sight on the bottom. The weapon is designed to launch syringes at long range after the user hits the end with the palm of their hand.

Trivia

This weapon seems to keep to the regular Naruto design for projectile weapons by not actually being a gun, instead, while very reminiscent of a sniper rifle.